Can I use solar panels on my electric vehicle to generate power when I drive or parked? This is a question that I asked myself years ago and I was asked about this again recently. The short answer is, yes. The real underlying question is how much power can be generated using solar panels on a vehicle while it is sitting idle parked all day in the sun.
To be the most accurate the different types of solar panels need to be identified. In particular, the solar panels for this use would use the solar photovoltaic effect to use photons which stimulate the electrons in the panel, in the end generating electricity. If you are looking for more information on how this works you can check out thegreenage.co.uk for further reading.
Types of Solar Panels
There are three solar cells monocrystalline, polycrystalline, and amorphous. If you do not understand what this means, that is okay. The important part to take away from these types is that the solar cells are available in different cell structures. Monocrystalline and polycrystalline are similar as they are made from crystals and are either left separate or strung together in the case of polycrystalline. Amorphous cells use a thin layer of silicon. With each type of solar cell there are advantages and disadvantages which include rigidity, low light ability, cost, and efficiency to generate power.
Monocrystalline  Polycrystalline  Amorphous 
Semiflexible / Rigid  Semiflexible / Rigid  Bendable 
1524%  1318%  79% 
To provide the best chance to charge deep cycle batteries, the most available area will be assumed for this case study. I will use a 2002 Ford Ranger regular cab 4×2 with a hard cover over the bed. In this case, the solar panels would be mounted on the cab roof and over the bed. It is worth mentioning that a custom framework would have to be fabricated to mount all the solar panels as well as route all wires to a battery charging device. The battery charger would have to protect the batteries from overcharging.
The area available for solar panels on the bed of a short wheelbase, as known as a 6foot bed, would be 77 inches by 52 inches. On the cab roof there would be 52 inches by approximately 35 inches for solar panels. These sizes are based on the truck dimensions found here.
To give the best result for the solar charging I have selected a monocrystalline solar panel which is semiflexible. This will keep the thickness of the panel low, which would in turn keep the change in air drag at a minimum. The solar panel is listed as 41.7” x 21.3” x 0.12” thick. With this particular solar panel, it would mean that one panel can be mounted on the cab roof and three can be mounted on the bed hard cover. As for the solar panel coverage, area this works out to be 3,553 square inches or 2.29 square meters.
Solar Panel Charging Equation
The equation (found at photovoltaicsoftware.com) to find the energy generated from solar panel system is the following, E = A * r * H * PR and can be in this equation E is the total energy generated in kWh units. A is the total solar panel area in meters squared, m². The solar cell efficiency that is listed above is the r unit as a percentage. The H unit is the annual average solar radiation on tilted panels, which is dependant on your geographic location. The solar radiation data for your region has already been collected and is available in a database from photovoltaicsoftware. The last variable is performance ratio (PR) for all the variables that effect the losses of the system which include losses due to the cables, converter, dust, and temperature losses, to mention a few.
E = A * r * H * PR
To plug in some of the holes of this equation I’m going to make some assumptions for H and PR. The solar radiation for each area will be different and will effect the energy generated. With that being stated again, I have selected Atlanta, Georgia for the H value, which has an annual average of 5,080 Wh/m²/day or 5.08 kWh/m²/day. For the performance ratio (PR) the percent of losses from all the equipment outside of the panels itself to be 75%, as the default value.
Using the equation now with the following variables:
A= 2.92 meters squared
r= 0.20 or (20% which is the mean value between 15% and 24%)
H= 5.08 kWh/m²/day for Atlanta, Georgia
PR = 0.75 or (75% performance efficiency)
E= 2.225 kWh
P= E / t
t= 12 hours of average sunlight per day for Atlanta, Georgia
P= 0.185 kW
This is assuming the vehicle is left outside during the whole day, either at home or work. There is an average of 12 hours of daylight in Atlanta. The power generated is 0.185 kW which is calculated by dividing the energy generated over the course of the day over the amount of average daylight. Also worth noting, the energy generated is an average, so the energy produced will be higher and lower depending on the time of year and amount of clouds.
With the solar charge from a full day of being in the sun has been determined, the amount of power used to operate the vehicle needs to be determined. For this case, I am first going to assume that this vehicle is used for a daily commuter. The length of driving from home to work and back can vary for everyone. I am going to assume that a half an hour oneway trip to work for this case. So in total an hour a day for each workday.
Vehicle Power Usage Estimate
There are many factors that will determine the power required to operate the electric vehicle conversion. Some of these factors include: transmission, average vehicle speed, acceleration (which depends on driving style), the difference of overall weight from the original pre conversion weight, and size of motor, or if there are two motors. There are more factors that affect the power required to operate the vehicle, these are the largest factors.
Assume the use of one AC50 electric motor running with a 72 volts system. The vehicle speed is assumed to be at highway speed of 65 mph or 105 kph and an automatic transmission. The motor speed is estimated to be at 2,550 revolutions per minute which would be required to be at highway speeds, as shown on another post for EV conversion transmission analysis and selection. The current is estimated to be 620 amps and voltage is 75 volts, as per the AC50 motor performance chart. As a result, the required power to operate the vehicle at highway speeds is 46.50 kW.
P_{hwy}= 46.50 kW
So the energy required for a commute in one direction will be 23.25 kWh since it is half an hour or 0.5 hours. A total round trip would end up being 46.50 kWh. This would be the worst case scenario for a half hour commute.
The best scenario would be a city commute traveling at 30 mph or 50 kph. With everything else the same, the motor would only need to run at approximately 1180 revolutions per minute to get to city speeds. Assuming constant speed for the duration of the commute, the current is estimated to be 450 amps and voltage at 75 volts. The power required to operate the vehicle at city speeds is 33.75kW.
P_{city}= 33.75 kW
The energy consumed for both highway and city scenarios are the same values as power due to totaling one hour of power usage, 46.50 kWh and 33.75 kWh respectively.
If you are looking for a refresher on power (kW) and energy (kWh) you can check out energylens.com for more information. A quick glance is that power, is work whether consumed or generated, and energy is power with a unit of time.
Results for EV with Solar Panels
Looking at the energy used and generated on an ideal day we can determine the efficiency of the solar panel charging system with regards to the electric vehicle demands. For the highway commute, the solar panels will generate 2.225 kWh, or 4.8 percent of the energy used in the day. Another way to state this is that if you are planning to charge solely with onboard solar this will take 21 days between drives.
For the city commute, the solar panels will generate 2.225 kWh, or 6.6 percent of the energy used in a day. Again, if you are planning to charge solely with an onboard solar system this will take 15 days between drives.
This could be a good option for those who are concerned more about how the electricity is produced over the cost of the panels. A small investment in the panels may take a while to return the initial investment. This can provide a little more peace of mind knowing that the electricity is renewable.
Here are some other articles if you are looking for more information:

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